Active linear amplifier inside transmitter module

Abstract

In one example embodiment, a transmitter module includes a header electrically coupled to a chassis ground. First and second input nodes are configured to receive a differential data signal. A buffer stage has a first node coupled to the first input node and a second node coupled to the second input node. An amplifier stage has a fifth node coupled to a third node of the buffer stage and a sixth node coupled to a signal ground that is not coupled to the chassis ground. An optical transmitter has an eighth node coupled to a seventh node of the amplifier stage and a ninth node configured to be coupled to a voltage source. A bias circuit is configured to couple a fourth node of the buffer stage to a bias current source.

What is claimed is: 
     
       1. A transmitter module comprising:
 a buffer circuit including a differential amplifier configured to receive a differential signal including a first input signal and a second input signal complementary to the first input signal and to output a single-ended signal on an output node; 
 a bias circuit coupled to the buffer circuit, the bias circuit including a thermal chirp compensation circuit; 
 an amplifier circuit coupled to the output node and configured to linearly amplify the single-ended signal; and 
 an optical transmitter coupled to the amplifier circuit and configured to be driven by the amplified single-ended signal. 
 
     
     
       2. The transmitter module of  claim 1 , further comprising a header, upon which the differential amplifier, the amplifier circuit, and the optical transmitter are mounted, the header being electrically coupled to a chassis ground, wherein the amplifier circuit is not coupled to the chassis ground. 
     
     
       3. The transmitter module of  claim 2 , wherein the amplifier circuit is coupled to a signal ground that is not coupled to the chassis ground. 
     
     
       4. The transmitter module of  claim 1 , wherein the buffer circuit further includes a buffer transistor coupled between the differential amplifier and the amplifier circuit. 
     
     
       5. The transmitter module of  claim 1 , wherein, in operation, the first and second input signals are received from a laser driver configured to perform waveform shaping on the first and second input signals and the linearly amplified single-ended signal preserves the waveform shaping performed by the laser driver. 
     
     
       6. A transmitter optical subassembly that includes the transmitter module of  claim 1 . 
     
     
       7. A transmitter module comprising:
 a differential amplifier including:
 a first differential transistor that includes a base, the base configured to receive a first input signal of a differential signal pair; 
 a second differential transistor that includes a base, the base configured to receive a second input signal of the differential signal pair that is complementary to the first input signal; 
 a first emitter resistor coupled between an emitter of the first differential transistor and a current source; 
 a second emitter resistor coupled between an emitter of the second differential transistor and the current source; 
 a first collector resistor coupled to a collector of the first differential transistor at a first node; and 
 a second collector resistor coupled to a collector of the second differential transistor at a second node, the first and second collector resistors being coupled to a third node; 
 
 a linear amplifier circuit configured to receive a single-ended signal provided by the first node; 
 a bias circuit including a thermal chirp compensation circuit, the bias circuit being coupled to the third node and the bias circuit being configured to provide an adjusted bias voltage to the third node; and 
 an optical transmitter coupled to the linear amplifier circuit. 
 
     
     
       8. The transmitter module of  claim 7 , further comprising a header, upon which the differential amplifier, the linear amplifier circuit, and the optical transmitter are mounted, the header being electrically coupled to a chassis ground, wherein the linear amplifier circuit is not coupled to the chassis ground. 
     
     
       9. The transmitter module of  claim 7 , further comprising a buffer circuit that includes the differential amplifier, the buffer circuit coupled to the linear amplifier circuit and configured to provide the single-ended signal to the linear amplifier circuit. 
     
     
       10. The transmitter module of  claim 9 , wherein the buffer circuit further comprises a buffer transistor, a base of the buffer transistor coupled to the first node and an emitter of the buffer transistor coupled to the linear amplifier circuit. 
     
     
       11. The transmitter module of  claim 10 , wherein the emitter of the buffer transistor is further coupled to a buffer resistor and a collector of the buffer transistor is coupled to a voltage source. 
     
     
       12. The transmitter module of  claim 10 , wherein the linear amplifier circuit includes a amplifying transistor, a base of the amplifying transistor coupled to the emitter of the buffer transistor and a collector of the amplifying transistor coupled to the optical transmitter.